The proposed study is designed to determine whether or not the secretory activity of the epinephrine and norepinephrine cells of the adrenal medulla of the cat is regulated by different neural populations in the hypothalamus and/or mesencephalon. Discrete loci in the hypothalamus and mesencephalon will be stimulated electrically with stereotaxically placed bipolar-electrodes. The entire hypothalamus and mesencephalon will be systematicaly explored at approximately 1mm intervals with precise histological localization of stimulus sites. Adrenal venous blood catecholamines will be differentially assayed using an automated trihydroxyindole fluorometric method. Blood pressure and other autonomic functions will also be monitored. Sites found to elicit the selective secretion of either adrenal epinephrine or norepinephrine will be investigated in order to determine the pharmacologic nature of the neurons involved. This will be accomplished by superfusion of limited areas of the C.N.S. with drugs which influence catecholaminergic, cholinergic and seratonergic mechanisms by means of push-pull cannulae and determining their effect on the adrenal secretory response to electrical stimulation of the C.N.S.